Showing papers on "Fresnel zone published in 2019"
TL;DR: A Phase-Reversal FZP (PR-FZP) made of Polylactic Acid (PLA) manufactured with a commercial 3D printer is proposed as a better, more efficient and MRI compatible alternative to conventional Soret FZPs.
Abstract: The development of flat acoustic lenses for different applications such as biomedical engineering is a topic of great interest. Flat lenses like Fresnel Zone Plates (FZPs) are capable of focusing energy beams without the need of concave or convex geometries, which are more difficult to manufacture. One of the possible applications of these type of lenses is tumor ablation through High Intensity Focused Ultrasound (HIFU) therapies with real time Magnetic Resonance Imaging (MRI) monitoring. In order to be MRI compatible, the FZP material cannot have electromagnetic interaction. In this work, a Phase-Reversal FZP (PR-FZP) made of Polylactic Acid (PLA) manufactured with a commercial 3D printer is proposed as a better, more efficient and MRI compatible alternative to conventional Soret FZPs. Phase-Reversal lenses, unlike traditional FZPs, take advantage of all the incident energy by adding phase compensation regions instead of pressure blocking regions. The manufactured PR-FZP achieves 21.9 dB of focal gain, which increases the gain compared to a Soret FZP of its same size by a factor of 4.0 dB. Both numerical and experimental results are presented, demonstrating the improved focusing capabilities of these types of lenses.
69 citations
TL;DR: In this paper, a 3-D printed circularly polarized (CP) modified Fresnel lens antenna operating at 300 GHz is introduced by virtue of the superior geometric flexibility of the 3D printing technique.
Abstract: In this paper, a novel 3-D printed circularly polarized (CP) modified Fresnel lens antenna operating at 300 GHz is introduced By virtue of the superior geometric flexibility of the 3-D printing technique, a modified Fresnel lens consisting of subwavelength discrete dielectric posts in the odd-numbered Fresnel zones is proposed It is further demonstrated that by integrating dielectric anisotropic metamaterial, the modified Fresnel lens can realize CP radiation fed by a simple linearly polarized (LP) open-ended waveguide (OEWG) The 3-D printing approach is also investigated to push the performance envelops of the 3-D printer for realization of the terahertz CP lens The measured results show that the axial ratios (ARs) of the fabricated antenna prototype are smaller than 3 dB from 265 to 320 GHz Moreover, the modified Fresnel lens has a maximum gain of 274 dBic, which is 09 dB larger than that of the conventional Fresnel zone plane antenna (FZPA) These validate the concept, the design, and the fabricated prototype
58 citations
TL;DR: A nanoengineered nonlinear metasurface based optical element that acts as an emitting Fresnel zone plate of terahertz (THz) waves generates broadband THz radiation and focuses each generated frequency on a different focal point along the optical axis, achieving a narrow beam waist and spectral selectivity of both the bandwidth and central frequency.
Abstract: We introduce a nanoengineered nonlinear metasurface based optical element that acts as an emitting Fresnel zone plate of terahertz (THz) waves. We show that the nonlinear zone plate generates broad...
40 citations
TL;DR: Two simple and high-efficiency techniques for measuring the orbital angular momentum (OAM) of paraxial laser beams are proposed and studied numerically and experimentally.
Abstract: Two simple and high-efficiency techniques for measuring the orbital angular momentum (OAM) of paraxial laser beams are proposed and studied numerically and experimentally. One technique relies on measuring the intensity in the Fresnel zone, followed by calculating the intensity that is numerically averaged over angle at discrete radii and deriving squared modules of the light field expansion coefficients via solving a linear set of equations. With the other technique, two intensity distributions are measured in the Fourier plane of a pair of cylindrical lenses positioned perpendicularly, before calculating the first-order moments of the measured intensities. The experimental error grows almost linearly from ~1% for small fractional OAM (up to 4) to ~10% for large fractional OAM (up to 34).
36 citations
TL;DR: In this article, a metasurface zone plate in which rings are composed of subwavelength antenna arrays is proposed to individually control amplitude, phase and polarization by the consistent material platform.
Abstract: Fresnel zone plates consisting of multiple concentric rings have been realized by tailoring amplitude, phase and polarization of light, but conventional Fresnel zone plates require totally different materials to control each property reducing light controllability. Here, a metasurface zone plate in which rings are composed of subwavelength antenna arrays is proposed to individually control amplitude, phase and polarization by the consistent material platform of metasurfaces. Hence, versatile degrees of freedom can be achieved to focus electromagnetic waves. We verify that dielectric metasurfaces can generate arbitrary poloarization states to cover the whole Poincare sphere in the visible regime, allowing light manipulation in the vectorial regime, which is not feasible by a conventional single liquid crystal film. Experimental demonstration of a polarization-modulated metasurface zone plate confirms the functional capability of dielectric metasurfaces exhibiting higher focusing efficiency than amplitude-modulated zone plates. Fresnel zone plates are capable of manipulating the amplitude, phase and polarization of light, but conventional designs require different materials for each functionality. Here, metasurface zone plates consisting of subwavelength antenna arrays, capable of efficient, multifunctional control from a single material, are presented.
31 citations
TL;DR: This paper deals with the classical question of estimating achievable resolution in terms of configuration parameters in inverse source problems, where a strip source is to be reconstructed from its radiated field observed over a bounded rectilinear domain parallel to the source.
Abstract: This paper deals with the classical question of estimating achievable resolution in terms of configuration parameters in inverse source problems. In particular, the study is developed for two-dimensional prototype geometry, where a strip source (magnetic or electric) is to be reconstructed from its radiated field observed over a bounded rectilinear domain parallel to the source. Resolution formulas are well known when the field is collected in the far field or in the Fresnel zone of the source. Here, the plan is to expand those results by removing the geometrical limitations due to the far field or Fresnel approximations. To this end, the involved radiation operators are recast as Fourier-type integral operators upon introducing suitable variable transformations. For magnetic sources, this allows one to find a closed-form approximation of the singular system and hence to estimate achievable resolution, the latter given as the main beam width of the point-spread function. Unfortunately, this does not happen for electric currents. In this case, the radiation operator is inverted by a weighted adjoint inversion method (a back-propagation-like method) that directly allows one to find an analytical expression of the point-spread function and hence of the resolution. The derived resolution formulas are the same for magnetic and electric currents; they clearly point out the role of geometrical parameters and coincide with the one pertaining to the Fresnel zone when the geometry verifies the Fresnel approximation. A few numerical examples are also enclosed to check the theory.
27 citations
TL;DR: A method for creating a three-dimensional array of focal spots by combination of a multi-focal diffractive lens and a two-dimensional multi-value phase grating, which creates five focal planes with a equal energy distribution in each plane.
Abstract: We demonstrate a method for creating a three-dimensional (3D) array of focal spots by combination of a multi-focal diffractive lens and a two-dimensional multi-value phase grating. The multi-focal Fresnel-based lens is created by means of encoding special nonlinearities into the phase structure of a Fresnel zone plate and is represented as a mathematical superposition of this phase function with a refractive lens. The imposed nonlinearity type enables the creation of multiple focal spots with uniform intensity along the optical axis. We demonstrate the example of a 3D multi-value phase grating, which creates five focal planes with a $5 \times 5$5×5 transverse array of focal spots with equal energy distribution in each plane. Experimental results are included to verify the theoretical outcomes, where the phase pattern of a 3D multi-value phase grating is encoded onto a spatial light modulator.
21 citations
TL;DR: It is shown that the diffraction of a vortex beam from an elliptic Gaussian aperture at the far-field regime forms a light beam that belongs to a family of light beams the authors call elegant elliptical vortex Hermite-Gaussian beams.
Abstract: In this work, a comprehensive analytic study of the diffraction of vortex beams from structured apertures is presented. We formulate the near- and far-field diffraction of a vortex beam from an aperture having an arbitrary functionality in the Cartesian coordinates by two general and different approaches. We show that each of the resulting diffraction patterns can be determined by a number of successive derivatives of the 2D Fourier transform of the corresponding hypothetical aperture function or equally can be obtained by a summation of 2D Fourier transforms of the corresponding modified aperture function. We implement both introduced analytic approaches in predicting the diffraction of a vortex beam from an elliptic Gaussian aperture, an elliptic Gaussian phase mask, and a hyperbolic Gaussian phase mask in the near- and far-field regimes. It is shown that the predicted diffraction patterns by both these approaches are exactly the same. It is shown that the diffraction of a vortex beam from an elliptic Gaussian aperture at the far-field regime forms a light beam that belongs to a family of light beams we call elegant elliptical vortex Hermite–Gaussian beams. In addition, the diffractions of a vortex beam from a Fresnel zone plate in general form for the on- and off-axis situations are formulated, and sinusoidal and binary zone plates are investigated in detail. Our general analytic formula can be used for a large variety of apertures including off-center situations and asymmetrical cases.
19 citations
TL;DR: A novel approach for fast ptychography scans over an extended field of view by means of simultaneous Fresnel zone plate and sample motion is presented.
Abstract: Scanning X-ray microscopy such as X-ray ptychography requires accurate and fast positioning of samples in the X-ray beam. Sample stages often have a high mobile mass as they may carry additional mechanics or mirrors for position measurements. The high mobile mass of a piezo stage can introduce vibrations in the setup that will lead to imaging quality deterioration. Sample stages also require a large travel range which results in a slow positioning step response and thus high positioning overhead. Moving lightweight X-ray optics, such as focusing Fresnel zone plates, instead of the sample can improve the situation but it may lead to undesired variations in the illumination probe which may result in reconstruction artifacts. This paper presents a combined approach in which a slow sample stage mechanism covers the long distance range for a large field of view, and a light-weight optics scanner with a small travel range creates a superimposed motion to achieve a fast step response. The step response in the ptychographic tomography instrument used was thereby improved by an order of magnitude, allowing for efficient measurement without loss of imaging quality.
18 citations
Posted Content•
TL;DR: In this article, a modified hologram reconstruction mechanism is presented which introduces the single shot capability in Fresnel incoherent correlation holography (FINCH) in inline configuration requires an active phase modulator and at least three camera shots to reconstruct objects without the twin image and bias terms.
Abstract: Fresnel incoherent correlation holography (FINCH) is a self-interference based super-resolution three-dimensional imaging technique. FINCH in inline configuration requires an active phase modulator and at least three camera shots to reconstruct objects without the twin image and bias terms. In this study, FINCH is realized using a randomly multiplexed bifocal binary Fresnel zone lenses fabricated using electron beam lithography. A modified hologram reconstruction mechanism is presented which introduces the single shot capability in FINCH. A point spread hologram library was recorded using a point object located at different axial locations and an object hologram was recorded. The image of the object at different planes were reconstructed using decorrelation of the object hologram by the point spread hologram library. Application potential including bio-medical optics is discussed.
17 citations
TL;DR: In this article, two birefringent Fresnel zone plates (FZPs) are embossed and a lens is formed by assembling the FZPs in a twisted nematic cell and filling the cell with a nematic crystal index matched to the reactive mesogen.
Abstract: Reactive mesogens (RMs) have found their way into different branches of science and application. They can be processed as standard liquid crystals and can then be polymerised to stabilise their shape and anisotropic properties. Their birefringence is used in optical compensation films while the complex director field is exploited for actuators. However, creating complex shapes while maintaining good alignment is a challenge in these applications. In the present work, the embossing of reactive mesogens is introduced. Embossing is a fast and large-scale method, which allows to form a large variety of structured reactive mesogen devices. To create a polarisation-independent lens, two birefringent Fresnel zone plates (FZPs) are embossed. A lens is formed by assembling the FZPs in a twisted nematic cell and filling the cell with a nematic crystal index matched to the RM. The device can be switched from a non-focusing to a focusing state by applying a small voltage. After characterising the efficiency and beam properties, the method is used to fabricate a switchable multi-level Fresnel zone plate with optical efficiencies beyond 50%. Finally, manufactured polarisation-independent gratings and microlens arrays are presented using the method to illustrate the wide range of applicability.
TL;DR: The problem of reconstructing a strip electric current from its radiated field collected over a bounded finite rectilinear observation domain, orthogonal and centered with respect to the source, is dealt with and the main idea is to rewrite the involved radiation operator as a Fourier-type integral operator by introducing a suitable variable transformation.
Abstract: The problem of reconstructing a strip electric current from its radiated field collected over a bounded finite rectilinear observation domain, orthogonal and centered with respect to the source, is dealt with. In particular, the study is developed for a two-dimensional, scalar geometry and focuses on the estimation of achievable performance in terms of the number of degrees of freedom (NDF) and depth resolution. This is a classical problem that we contributed to in the past by addressing a Fresnel zone configuration. Here, the plan is to expand those results by removing the geometrical limitations due to the Fresnel approximation. The main idea is to rewrite the involved radiation operator as a Fourier-type integral operator by introducing a suitable variable transformation. This allows applying simple Fourier-based reasoning to estimate the achievable point-spread function, which in turn is used to estimate the NDF and depth resolution. The obtained NDF and depth resolution estimations are compared to those returned by numerical computation of the relevant singular value decomposition, and very good agreement is found. Moreover, it is shown that the results obtained for the Fresnel zone are a particularization of the new findings when such an approximation holds true.
TL;DR: In this paper, it was shown that parallel strips of phase-changing material, or "noodles," generically produce parabolic structures in the delay-rate domain, such as scintillation arcs for many pulsars.
Abstract: I show that narrow, parallel strips of phase-changing material, or "noodles," generically produce parabolic structures in the delay-rate domain. Such structures are observed as "scintillation arcs" for many pulsars. The model assumes the strips have widths of a few Fresnel zones or less, and are much longer than they are wide. I use the Kirchhoff integral to find the scattered field. Along the strips, integration leads to a stationary-phase point where the strip is closest to the line of sight. Across the strip, the integral leads to a 1D Fourier transform. In the limit of narrow bandwidth and short integration time, the integral reproduces the observed scintillation arcs and secondary arclets. The set of scattered paths follows the pulsar as it moves. Cohorts of noodles parallel to different axes produce multiple arcs, as often observed. A single strip canted with respect to the rest produces features off the main arc. I present calculations for unrestricted frequency ranges and integration times; behavior of the arcs matches that observed, and can blur the arcs. Physically, the noodles may correspond to filaments or sheets of over- or under-dense plasma, with a normal perpendicular to the line of sight. The noodles may lie along parallel magnetic field lines that carry density fluctuations, perhaps in reconnection sheets. If so, observations of scintillation arcs would allow visualization of magnetic fields in reconnection regions.
TL;DR: Fresnel zone plates for nano-ARPES in the extreme ultraviolet regime have been fabricated and tested and provide high photon flux combined with spot sizes down to 0.4 µm.
Abstract: This article reports on the fabrication and testing of dedicated Fresnel zone plates for use at the nano-ARPES branch of the I05-ARPES beamline of Diamond Light Source to perform angle-resolved photoelectron spectroscopy with sub-micrometre resolution in real space. The aim of the design was to provide high photon flux combined with sub-micrometre spot sizes. The focusing lenses were tested with respect to efficiency and spatial resolution in the extreme ultraviolet between 50 eV and 90 eV. The experimentally determined diffraction efficiencies of the zone plates are as high as 8.6% at 80 eV, and a real-space resolution of 0.4 µm was demonstrated. Using the zone-plate-based setup, monolayer flakes of the two-dimensional semiconductor WS2 were investigated. This work demonstrates that the local electronic structure can be obtained from an area of a few micrometres across a two-dimensional heterostructure.
TL;DR: In this paper, a binary zone plate design strategy was proposed to generate arbitrary illuminations for coherent multiplexing, structured illumination, and wavefront shaping experiments, where the duty cycle, harmonic order, and zone placement were adjusted to vary both the amplitude and phase of the wavefront at the lens.
Abstract: Diffractive lenses fabricated by lithographic methods are one of the most popular image forming optics in the x-ray regime. Most commonly, binary diffractive optics, such as Fresnel zone plates, are used due to their ability to focus at high resolution and to manipulate the x-ray wavefront. We report here a binary zone plate design strategy to form arbitrary illuminations for coherent multiplexing, structured illumination, and wavefront shaping experiments. Given a desired illumination, we adjust the duty cycle, harmonic order, and zone placement to vary both the amplitude and phase of the wavefront at the lens. This enables the binary lithographic pattern to generate arbitrary structured illumination optimized for a variety of applications such as holography, interferometry, ptychography, imaging, and others.
TL;DR: In this article, a multiline structure of segmented grooves with dimensions derived from Fresnel zones was used for focusing surface plasmon polaritons at a Fresnel-type grating coupler.
Abstract: Time-resolved photoemission microscopy is used to investigate the spatiotemporal properties of surface plasmon polaritons launched at a Fresnel-type grating coupler. By milling a multiline structure of segmented grooves with dimensions derived from Fresnel zones into a plasmonic material, efficient focusing of surface plasmon polaritons can be accomplished. We demonstrate the presence of pulse broadening at the focus associated with propagation delays in the device. Moreover, our experimental data implies an enhancement of the plasmonic field energy density at the focus in excess of a factor of 10, with a focal spot size at the Abbe limit for our lens.
Patent•
23 May 2019
TL;DR: In this article, a batch processing method for fabrication of diffractive optics is disclosed, having applicability to high resolution ultra-high aspect ratio Fresnel Zone Plates for focusing of X-rays or gamma-rays having energies up to hundreds of keV.
Abstract: A batch processing method for fabrication of diffractive optics is disclosed, having applicability to high resolution ultra-high aspect ratio Fresnel Zone Plates for focusing of X-rays or gamma-rays having energies up to hundreds of keV. An array of precursor forms comprising columns is etched into a planar substrate. After sidewall smoothing, a nanolaminate, comprising a sequence of alternating layers of different complex refractive index, is deposited on the sidewall of each column by atomic layer deposition (ALD), to define a specified diffractive line pattern around each column, to form a binary or higher order diffractive optic. After front surface planarization and thinning of the substrate to expose first and second surfaces of the diffractive line pattern of each diffractive optic, the height h in the propagation direction provides a designed absorption difference and/or phase shift difference between adjacent diffractive lines. Optionally, post-processing enhances mechanical, thermal, electrical and optical properties.
TL;DR: Flexible, lightweight, four- and eight-level phase photon sieves with 25.8% and 49.7% transmission efficiency, respectively, up to five times greater than that of any other photon sieve reported thus far are presented.
Abstract: Over the past several decades, the need for high-resolution, high-efficiency, lightweight, high-contrast focusing optics has continued to increase due to their applications in fields such as astronomy, spectroscopy, free-space optical communications, defense, and remote sensing. In recent years, photon sieve planar diffractive optics, which are essentially Fresnel zone plates with the rings broken into individual “pinhole” apertures, have been developed on flexible, lightweight polyimide substrates. However, transmission efficiencies have continuously been very low (∼1%–11%) until this work, thus impeding the widespread use of photon sieves in practical applications. Here, we present flexible, lightweight, four- and eight-level phase photon sieves with 25.7% and 49.7% transmission efficiency, respectively, up to five times greater than that of any other photon sieve reported thus far. Additionally, these sieves were fabricated via a single step pulsed laser ablation method. The total time to fabricate a ∼3 cm2 photon sieve via the single-step fabrication was tens of seconds, giving the technique a significant advantage over traditional photolithography used to generate multilevel structures. Analytical analysis of the photon sieve was carried out via the finite-difference time-domain (FDTD) method and was in very good agreement with experimental results. We have also calculated via FDTD modeling the behavior of higher-level photon sieves for further enhanced efficiencies, and analytically show an estimated upper bound on photon sieve efficiency of 70% within the first focal plane null in the limit of increasing step number, and the data presented herein provide a relationship between efficiency and step number. Additionally, this process of multilevel diffractive lens fabrication can be extended to multilevel Fresnel zone plates, which have not previously been demonstrated by this process. The results presented in this work represent a new step in high-resolution diffractive optics, showing efficiencies suitable for widespread applications in addition to drastically reducing the cost and complexity of fabricating multilevel focusing elements.
TL;DR: In this paper, the phase retrieval from single-shot Fresnel zone irradiance data is studied and it is shown that a simplistic Gerchberg-Saxton (GS) type iterative approach fails to produce accurate phase retrieval.
Abstract: We report simulation results on phase retrieval from single-shot Fresnel zone irradiance data. It is shown that a simplistic Gerchberg–Saxton (GS) type iterative approach fails to produce accurate ...
TL;DR: In this paper, the 3D Fresnel zones are calculated from the transmitter (Tx) source to each cell on a raster digital map and the attenuation and phase shift of each segment can be adjusted according to the obstacle type.
Abstract: This article discusses the Fresnel radio tool (FRT) model for radio-coverage prediction based on the Fresnel-zone calculation. The 3D Fresnel zones are calculated from the transmitter (Tx) source to each cell on a raster digital map. For numerical calculation purposes, Fresnel zones are cross sectioned to a finite number of fragments. The attenuation and phase shift of each segment can be adjusted according to the obstacle type. At the target receiver (Rx) point, contributions from each fragment, represented by complex numbers, are summed and converted to a signal strength.
01 May 2019
TL;DR: A measurement solution and image reconstruction algorithms using radio-frequency tomography to determine the position of a man in closed rooms using Bluetooth 4.0 Low Energy signals and devices emitting radio signals.
Abstract: The article presents a measurement solution and image reconstruction algorithms using radio-frequency tomography. In this method, the action requires measuring the strength of the radio signal between the transmitter and the receiver. The under pressure of the measurement value of the signal strength changes as a result of the absorption, reflection or dissipation of electromagnetic waves. Radio tomography can determine the position of a man in closed rooms. It can be used for navigation and locating inside buildings. The solution works on the basis of Bluetooth 4.0 Low Energy signals and devices emitting radio signals.
TL;DR: A fast method for measuring the radar cross section of a complex target at non-normal incidences and Fresnel region antenna-to-target distances using a very simple measuring configuration consisting of two horn antennas and a vector network analyzer.
Abstract: In this paper, we propose a fast method for measuring the radar cross section of a complex target at non-normal incidences and Fresnel region antenna-to-target distances. The proposed method relies both on the physical optics approach and on averaging the field distribution over the transmitting and receiving antenna apertures. The ratio between the analytical expression of the radar cross section at far-field and Fresnel region results in a field-zone extrapolation factor. The RCS resulting from the scattering parameters measured at Fresnel region distances is then corrected with that field-zone extrapolation factor. The method is suitable to be used in a perturbed, multipath environment by applying the distance averaging technique, coupling subtraction or time gating. Our technique requires a very simple measuring configuration consisting of two horn antennas and a vector network analyzer. The experimental validation of the proposed technique demonstrates reasonable agreement with simulated radar cross section at non-normal incidence.
DOI•
25 Aug 2019
TL;DR: In this article, the phase variance of a small number of nanoslits was calculated using finite element numerical analysis and a transmission-enhanced Fresnel zone plate was designed by applying the phase characteristics from the small-number nanoslit model.
Abstract: We have studied the behavior of light in the intermediate regime between a single nanoslit and an infinite nanoslit array. We first calculated the optical characteristics of a small number of nanoslits using finite element numerical analysis. The phase variance of the proposed nanoslit model shows a gradual phase shift between a single nanoslit and ideal nanoslit array, which stabilizes before the total array length becomes ~0.5 λ. Next, we designed a transmission-enhanced Fresnel zone plate by applying the phase characteristics from the small-number nanoslit model. The virtual-point-source method suggests that the proposed Fresnel zone plate with phase-invariant nanoslits achieves 2.34x higher transmission efficiency than a conventional Fresnel zone plate. Our report describes the intermediate behaviors of a nanoslit array, which could also benefit subwavelength metallic structure research of metasurfaces.
TL;DR: The results of simulating an image of a protein cell and its deconvolutionary processing are presented, before and after applying the "intensity restoration algorithm", which takes into account the absorption effect before standard deconVolution.
TL;DR: In this article, it was shown that narrow filaments or sheets of over- or under-dense plasma, or "noodles," with fluctuations of scattering phase of less than a radian, can form the scintillation arcs seen for many pulsars.
Abstract: We show that narrow filaments or sheets of over- or under-dense plasma, or "noodles," with fluctuations of scattering phase of less than a radian, can form the scintillation arcs seen for many pulsars. The required local fluctuations of electron density are indefinitely small. We assume a cosine profile for the electron column and find the scattered field by analytic Kirchhoff integration. For a large electron column, corresponding to large amplitude of phase variation, the stationary-phase approximation is accurate; we call this regime "ray optics". For smaller-amplitude phase variation, the stationary-phase approximation is inaccurate or inapplicable; we call this regime "wave optics". We show that scattering is most efficient when the width of the strip equals that of one pair of Fresnel zones, and in the wave-optics regime. We show that the resolution of present observations is about 100 Fresnel zones on the scattering screen. Incoherent superposition of strips within a resolution element tends to increase the scattered field. We find that observations match a single noodle per resolution element with phase of up to 12 radians; or many noodles per resolution element with arbitrarily small phase variation each, for net phase of less than a radian. Observations suggest a minimum radius for noodles of about 650 km, comparable to the ion inertial scale or the ion cyclotron radius in the scattering plasma.
TL;DR: In this paper, the authors proposed a method for optimizing the configuration of the Fresnel zone aperture, which reflects the influence of the diffraction of its shadow, and the sensitivity characteristics of an image sensor.
Abstract: As part of our ongoing research on lensless imaging with a Fresnel zone aperture (FZA), we propose a method for optimizing the configuration of the FZA, which reflects the influence of the diffraction of its shadow, and the sensitivity characteristics of an image sensor.
TL;DR: A dichroic dye-doped liquid crystal Fresnel lens was fabricated and investigated to observe the combination of phase and amplitude modulation based focusing, showing a significant 4% improvement in relative efficiency in the lens.
Abstract: A dichroic dye-doped liquid crystal Fresnel lens was fabricated and investigated to observe the combination of phase and amplitude modulation based focusing. An anthraquinone dichroic dye was doped into a liquid crystal host, which when in the Fresnel lens configuration, generates a Fresnel zone plate with alternating “transparent” and “opaque” zones. The zones were induced by using photo-alignment of a light-sensitive alignment layer to generate the alternating pattern. The voltage dependency of efficiency for the dye-doped and pure liquid crystal Fresnel devices were investigated. Incorporation of dyes into the device yielded a significant 4% improvement in relative efficiency in the lens, giving a maximum of 37% achieved in the device, much closer to the theoretical 41% limit when compared with the non-dye-doped device. The input polarization dependence of efficiency was also investigated, showing very small fluctuations (±1.5%), allowing further insight into the effect of fabrication method on these liquid crystal Fresnel devices.
TL;DR: Experiments at the DELTA synchrotron facility reveal a minimum spot size and resulting spatial resolution of 9±3 μm, which is the theoretical limit resulting from the synch rotatedron beam parameters at 60 eV photon energy.
Abstract: Zone plate design and efficient methods for the fabrication of zone plates for extreme ultraviolet (EUV) and soft x-ray applications in a newly developed scanning reflection microscope are presented. Based on e-beam lithography, three types of transmission zone plates with focal lengths between 6 and 15 mm are reported: (i) phase-shifting zone plates made by 190 nm thick PMMA rings on Si3N4 membranes, (ii) absorbing zone plates made by 75 nm thick Au ring structures on Si3N4, and (iii) freestanding Au rings of 50 nm thickness and increased transmission in the EUV range. Experiments at the DELTA synchrotron facility reveal a minimum spot size and resulting spatial resolution of 9±3 μm, which is the theoretical limit resulting from the synchrotron beam parameters at 60 eV photon energy. Images of a Ti/Si chessboard test pattern are recorded exploiting the energy dependence of the element-specific reflectance.
Patent•
19 Nov 2019
TL;DR: In this article, a phase recovery detection device and phase recovery method based on Fresnel zone plate diffraction information fusion is proposed. But the method is not suitable for the use of a traditional lens as a light beam convergence component, and utilizes a multi-focal characteristic of the Fresnel Zone Plating to make a collected diffraction light spot contain more information.
Abstract: The invention discloses a phase recovery detection device and a phase recovery method based on Fresnel zone plate diffraction information fusion. The device includes a laser, an attenuation mirror, amicroscope objective, a small-hole filter, a collimating objective, a to-be-measured component, a Fresnel zone plate, and an image acquisition device, which are sequentially arranged along a directionof an optical path. The device utilizes the Fresnel zone plate instead of a traditional lens as a light beam convergence component, and utilizes a multi-focal characteristic of the Fresnel zone plateto make a collected diffraction light spot contain more diffraction information. The method performs recovery by utilizing diffracted light intensity distribution modulated by the Fresnel zone plate,and can achieve reconstruction of a to-be-measured wavefront wider frequency band. The device is simple and can achieve acquisition of diffraction information in a wide frequency band without changing a defocus position, and the method has higher algorithm convergence speed and wavefront reconstruction precision, and is high in precision when a large wavefront errors in the wide frequency band isdetected.